Signature stackers are presently in wide-spread use for counting and stacking signatures and the like. Such signature stackers are typically provided with stacking platforms which are moved through the incoming signature stream to intercept the signature stream and collect signatures thereon when the platform previously receiving signatures has accumulated the desired number of signatures. The signatures collect on the stacking platform until the next stacking platform spaced therefrom is caused to intercept the signature stream whereupon the signatures are thereafter collected on said next stacking platform. The criteria for intercepting the signature stream is dependent upon the count of signatures desired to be collected on the previous stacking platform, which count is selected in accordance with the requirements of the user.
The stacking platform supporting the desired number of signatures drops out from beneath the accumulated stack enabling the stack thereon to fall between two assemblies mounted on a turntable and including a movable "picket fence" and pusher arms/gates arranged upon the turntable and moveable to push a completed batch from the turntable and delivery it to an associated conveyor. The turntable is then rotated through one half revolution prior to receipt of the next stack to form compensated bundles.
The stacking platform which is rapidly moved down from beneath the stack of signatures is eventually returned to the intercept position in readiness for intercepting the over-lapping signature stream when the next preceeding stacking platform has received the desired number of signatures.
The stacking platforms are driven by a heavy-duty motor controlled by control means to move the stacking platform a first velocity during stacking and as it returns to the intercept position and to reduce the motor output speed to thereby reduce the velocity of the stacking platform as it approaches the intercept position and thereafter to halt the stacking platform upon reaching the intercept ready or "home" position. The position of each stacking platform is continuously monitored by means of a gear whose angular velocity is a function of the instantaneous velocity of the stacking platform and a cooperating sensor for generating pulses upon sensing the teeth of said gear passing the sensor.
A reciprocating claw is arranged at the intercept-ready position so that a cam follower roller means associated with each stacking platform enters into the claw when the platform is in the intercept-ready position. A predetermined delay interval after the cam follower roller enters the claw, cylinder means coupled to the claw is activated causing the claw and cam follower roller to move in a direction transverse to the path of movement of the stacking platform whereupon the free ends of the stacking platform swing across the path of movement of the signature stream to abruptly intercept the signatures in the signature stream approaching the platform to assure that the number of signatures delivered to the stacking platform previously receiving signatures is equal to a predetermined count and so that those signatures following the last signature to be delivered to the stacking platform last receiving signatures are diverted from the stacking platform containing a completed stack and collected upon the stacking platform which has just intercepted the signature stream.
The aforementioned heavy-duty motor remains deenergized during the time that the claw swingably moves the stacking platform to the intercept position. The heavy-duty motor remains deenergized for a predetermined delay interval sufficient to assure that the last signature delivered to the stacking platform previously collecting signatures is properly received by and collected on said platform.
Upon termination of the aforementioned drop delay, the heavy-duty motor is reenergized causing the stacking platform now receiving signatures to move through the stacking region, collecting signatures from the incoming signature stream until the next stacking platform reaching the intercept ready position moves into the signature stream.
The velocity of the stacking platform moving through the stacking region is primarily a function of the number of signatures to be collected upon the stacking platform and the rate of flow of signatures to the stacker. Monitoring means including a microprocessor continuously monitors and updates the speed control value utilized to control the speed of movement of the stacking platform. The microprocessor generates a ramp signal for accelerating the platform from a standstill to the desired stacking velocity. The microprocessor, whenever possible, reduces the stacking speed of the stacking platform (once per completed stack) to an optimum value which is chosen to assure the formation of a neat stack, adjusting the speed control value a predetermined incremental amount prior to the formation of each subsequent signature stack. The use of a variable speed motor under the control of a microprocessor totally eliminates the need for clutch and brake assemblies typically utilized in prior art equipment and also provides more accurate and reliable control over the stacking operation.
The turntable assembly utilized to form compensated bundles is comprised of a solid unitary turntable having a pair of moveable "picket fence" assemblies each further including a plurality of pusher/gates which, together with the picket fence assemblies, form a receiving pocket for receiving and supporting signature stacks and preventing the signature stacks from toppling during the time that the turntable is rapidly rotated after the receipt of a signature stack and before the receipt of the next signature stack, to form compensated bundles.
Rotation of the turntable through one-half revolution after receipt of each signature stack and before the receipt of the next signature stack permits formation of a compensated bundle.
The turntable is mounted to rotate about a vertical axis. A cylinder assembly drives the turntable through one-half revolution and a cooperating shock absorber assembly, pivotably linked to the turntable operates in a complementary fashion relative to the air cylinder to decelerate and halt the turntable as it approaches the completion of one-half revolution.
Pressure sources of different pressure values are selectively coupled to the air cylinder to reduce the pressure applied to the air cylinder as it nears completion of one-half revolution thus assuring more accurate halting of the turntable.
A novel support for the turntable comprises a hollow cylindrical housing rigidly secured to the stacker main frame. A second hollow cylindrical housing is arranged within the first housing in a concentric manner and is rotatably secured therein by suitable bearings in order to enable the inner housing to rotate relative to the outer stationary housing while preventing the inner housing from experiencing any axial movement.
A variable speed servo motor is secured to the bottom end of the inner housing so as to be rotatable therewith. The variable speed servo motor output shaft is coupled to an intermediate shaft by a reducing gear assembly and a flexible coupling. The intermediate shaft is rotatably maintained along the axis of rotation of said inner housing by bearings and extends upwardly toward the underside of the turntable. A pair of sprockets are mounted at spaced intervals to the upper end of said intermediate shaft for driving a pair of closed-loop chains arranged along the underside of the turntable and each engaging a plurality of sprockets. Two of said plurality of sprockets each impart drive to one of the moving wall or "picket fence" assemblies each being comprised of additional upper and lower horizontally aligned chains having a pluarlity of "pickets" mounted therealong to form a "picket fence" or "moving wall". Pusher/gate elements are arranged at spaced intervals along each moving wall whereby a pair of said pusher/gate elements of each moving wall cooperatively form a signature stack receiving area with the moving walls of the two moving wall assemblies to retain the stack or stacks of signatures upright and prevent them from being displaced or toppling as a result of the rapid rotation of the turntable.
When a bundle of either compensated or uncompensated type is completed, the variable speed motor mounted beneath the turntable is energized to rotate the sprockets forming part of each moving wall assembly. The variable speed servo motor operates at a first, higher speed to push a bundle off of the turntable. Sensors sense the approach of the moving wall assembly toward completion of the pushing operation to reduce the speed of the motor, thereby assuring that the motor and hence the pusher/gates will be brought to a halt at the precisely desired position in readiness for receipt and formation of a new bundle.
Upon completion of the pushing operation to push the last completed bundle off of the turntable and upon a cooperating conveyor, the next stack of signatures is formed and deposited upon the turntable and between the movable walls and pusher/gates. After the deposit of said signature stack and before the deposit of the next signature stack, the variable speed servo motor mounted to the underside of the turntable is maintained deenergized and the air cylinder arranged beneath the turntable is operated to rotate the turntable through one-half revolution, in the same manner as previously described. These operations continue in a repetitive manner to successively form bundles of either the compensated or uncompensated type.